Conventionally, various types of thermosetting resin compositions have been used for insulating materials for printed-wiring boards and the like, and sealing materials for sealing semiconductors and the like. There is a demand for these thermosetting resin compositions to be excellent in the performance of electrical properties, heat resistance, and flame-retardancy, along with an improvement in the performance of various types of electronics and a diversification of applications.
In such a background, in order to improve properties of the thermosetting resin compositions, it has been proposed that a benzoxazine compound that has excellent electrical properties and heat resistance and is useful for provision of flame-retardancy is mixed into the thermosetting resin compositions as a resin component (see Patent Document 1, for example). It has been known that this benzoxazine compound is cured along with ring-opening polymerization of an oxazine ring in a process in which the thermosetting resin composition is hot molded. However, the benzoxazine compound has a slower cure rate compared to other thermosetting resins such as an epoxy resin and imide resin, and thus there is a problem in that if the benzoxazine compound is used as the component of the thermosetting resin, the benzoxazine compound is not sufficiently cured under hot molding conditions under which laminates or sealing materials are generally molded, and it is difficult for a cured material to have high heat resistance and a high glass transition point.
Also, it is possible to increase the degree of cure of the benzoxazine compound, improve the heat resistance of the cured material, and increase the glass transition point of the cured material through extending a molding time period or raising a molding temperature during hot molding. However, in that case, productivity decreases and manufacturing costs increase, and it is difficult to control resin fluidity and the like during molding, as a result of which molding properties may deteriorate. Thus, there is an issue in that the degree of freedom of designing hot molding conditions decreases.
Also, it has been conventionally proposed that a benzoxazine compound is mixed along with a phosphorus-containing compound into a thermosetting resin such as an epoxy resin or imide resin to prepare the thermosetting resin composition in order to become halogen-free and flame-retardant. However, if the content of the benzoxazine compound is increased, the cure rate of the resin decreases, and thus there is a concern that the above-described various issues may arise. On the other hand, if the content of the benzoxazine compound is reduced, there is an issue in that the properties of the benzoxazine compound are deteriorated.
In view of this, a phenol compound is used as the resin component in combination with the benzoxazine compound in order to accelerate curing of the benzoxazine compound, but the fact is that undercuring of the benzoxazine compound has not been sufficiently addressed.